RF-Pilot Based Frequency Offset Estimation and Phase Noise Compensation for CO-OFDM Systems

摘要

One of the most severe impairments that affect coherent optical systems employing high-order modulation formats is phase noise due to transmit and receive lasers. The vulnerable sensitivity to laser linewidth induced inter-carrier interference (ICI) has long been recognized as a major problem to coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems. Among the existing phase noise compensation algorithms, the RF-pilot aided phase recovery (RAPR) method shows a better compensation capability to laser linewidth. However, RAPR may fail to extract the pre-inserted RF-pilot at the receiver due to the influence of carrier frequency offset (CFO). An effective frequency offset estimation (FOE) is thus required to implement before performing RAPR. In consideration of the fact that the conventional FOE algorithm not only has high computational complexity, but more importantly cannot work in coordination with RAPR, a new RF-pilot aided frequency offset estimation (RAFOE) algorithm is proposed, in which CFO can be easily estimated by searching the peak of spectral samples. Furthermore, in order to obtain the optimum compensation performance with lower computing cost at combining RAFOE and RAPR, a joint frequency offset and phase noise compensation scheme is also performed in this paper.